In the manufacture of wound capacitors heretofore, such as of the metallized type, the final value of capacitance of each such capacitor has normally been controlled by one of the following three techniques: (1) winding the capacitor in accordance with a specified length of metallized film; (2) winding the capacitor in accordance with a specified number of revolutions of the winding arbor, or (3) winding the capacitor to a measured specified diameter.
Such indirect control over the final value of capacitance of a so-called "as wound" capacitor has resulted primarily because of circuit responsive speed limitations. More specifically, conventional capacitance measuring test sets employed heretofore, whether of the analog bridge-balancing type, or more recently of the digital type, have not been capable of making high speed repetitive capacitance measurements at rates on the order of 1,000 per second. Such high speed measurements are required, and must be performed "on-the-fly", i.e., dynamically, if a roll-type capacitor is to be continuously wound, at film speeds often in the range of one to 10 feet per second, until a final, precise value of capacitance has been ascertained.
In addition, prior capacitance measuring test sets, whether of the analog or digital type, have been quite expensive, typically costing in the range of three to eight thousand dollars, and have also not been adapted to make even low speed capacitance measurements with one side of the capacitor grounded. Such grounded measurements are required, of course, if capacitors of the metallized type are to be measured on-the-fly during the winding thereof on a metal arbor.
In view of the foregoing, it is readily seen that wound-to-length, wound-to-diameter or wound to a specified number of turns techniques have generally been employed in the high speed, high volume manufacture of roll-type capacitors heretofore and, in particular, those of the metallized, minaturized type. Unfortunately, such indirect control over the final value of capacitance of roll-type capacitors have often proven less than satisfactory, particularly because of the physical variations that inherently exist in film thickness over any appreciable unit length of film, as manufactured.